In a typical electrically switched liquid crystal display device, a film of liquid crystal material is sealed between two glass or plastic plates that are provided with transparent conducting electrodes. When a voltage is applied to the electrodes, the orientation of the liquid crystal is affected, altering the manner in which light is absorbed by polarizers attached to the cell or by dichroic dyes dissolved in the liquid crystal.
The cell construction and operation described above have several disadvantages. In most applications, the electrodes must be specially treated or prepared to align the liquid crystal in a particular way at the surface of the cell wall. Furthermore, it is difficult to fill and then seal the liquid crystal in the narrow region between the plates. Special techniques and materials are required for cell fabrication, particularly for mass production. Uniformity in cell thickness and preparation can be a problem and a limitation in large scale displays. The use of polarizers complicate cell construction, add to the cost and can limit the cell contrast or brightness in that they always absorb a component of incident light. Finally, the response time of a conventional liquid crystal display can be marginal for many applications.
Recent display technology has been directed toward overcoming some of these difficulties and limitations. One approach has been to develop materials which contain small regions of the liquid crystals with light scattering properties that can be electrically manipulated. Two types of such material have been suggested: materials containing encapsulated liquid crystals and materials with open or connected micropores which can be filled with liquid crystals. Such material would avoid the sealing problems of the conventional cell and could make it possible to construct large displays. Furthermore, polarizers are not required for the operation of this type of display, avoiding the limitations that dichronic polarizers create.
One prior art proposal for encapsulating liquid crystals, disclosed in French Pat. No. 2,139,537 dated Dec. 11, 1972, involves forming an aqueous emulsion of liquid crystal material with an immiscible binder such as polyvinyl alcohol. The mixture is emulsified in a high speed blender or the like to form droplets of the liquid crystal that are encapsulated by the binder. The encapulated droplets are then coated on a clear plastic substrate having the usual conducting electrodes. A similar technique is described in U.S. Pat. No. 4,435,047 issued Mar. 6, 1984.
A prior art proposal involving filling the open or connected micropores of a plastic sheet with a nematic or other type of liquid crystal is disclosed in U.S. Pat. No. 4,048,358 issued Sept. 13, 1977.